What geological condition can cause significant seasonal changes in indoor radon levels?

Karst geology is characterized by the dissolution of soluble rocks, such as limestone, which can create underground drainage systems and caves. This geologic condition significantly impacts the movement of groundwater and the transport of radon gas, which is produced naturally from the decay of uranium found in soil and rock.

In areas with karst geology, the porous nature of the rock can allow radon to accumulate in the subsurface before it enters buildings. Seasonal changes, such as variations in temperature and precipitation, can influence the groundwater levels and pressure changes in karst systems. During specific seasons, these conditions may lead to increased radon concentration as the gas is pushed through fractures and into occupied spaces.

This behavior is less likely in other geological conditions like volcanic activity, mountainous terrain, or glacial formations, where the characteristics of the rock and soil do not facilitate similar seasonal variations in radon levels as effectively as karst formations do. Therefore, karst geology is a significant factor in understanding seasonal fluctuations of indoor radon levels.